nephrin and pimagedine

Podocalyxin represents a Wilms' tumor suppressor protein (WT1)-regulated differentiation marker for glomerular epithelium. We provide evidence concerning mechanisms involved in the regulation of podocalyxin expression following long-term exposure to increased (25 mM) glucose levels. Prolonged culture of conditionally immortalized human podocytes in 25 mM glucose induced suppression of podocalyxin expression both at the protein and mRNA levels, whereas WT1 protein levels remained unaltered. WT1 interacted with another transcription factor, CRE-binding protein (CBP). This association was decreased by 40% in the presence of 25 mM glucose. Chromatin immunoprecipitation assays on chromatin from podocytes cultured in 25 mM glucose revealed reduced WT1 binding to podocalyxin promoter sequences, probably resulting from impaired WT1-CBP interactions. We explored the possible role of glucose-induced adducts (advanced glycation end products; AGEs) in impairing interactions between WT1 and CBP, with the use of aminoguanindine, an inhibitor of AGE formation. Podocytes were cultured in the simultaneous presence of 20 mM aminoguanidine and 25 mM glucose, and podocalyxin protein levels were examined. Aminoguanidine effectively prevented downregulation of podocalyxin protein levels but could not restore podocalyxin levels once expression was suppressed. Thus increased glucose apparently impaired the ability of WT1 to initiate transcription in part by decreased association of WT1 with CBP. Administration of aminoguanidine concomitant with increasing glucose levels in our in vitro model system protected from glucose-induced "silencing" of the podocalyxin gene, suggesting that AGEs play an important role in suppressing its expression in diabetic conditions.

Topics: Binding Sites; Cell Line, Transformed; Cyclic AMP Response Element-Binding Protein; Down-Regulation; Glucose; Glycation End Products, Advanced; Guanidines; Humans; Membrane Proteins; Phosphoproteins; Podocytes; Promoter Regions, Genetic; RNA, Messenger; Sialoglycoproteins; Sp1 Transcription Factor; Time Factors; Transcription, Genetic; WT1 Proteins; Zonula Occludens-1 Protein

Mutations in the gene coding for the podocyte slit-pore membrane protein, nephrin, are responsible for the Finnish-type congenital nephrotic syndrome. The present study sought to examine whether nephrin expression may also be altered in experimental diabetes, and how such changes related to the development of proteinuria. In addition, the study also sought to examine nephrin expression in animals treated with different anti-proteinuric therapies.. Nephrin gene expression and localization were examined in rats with streptozotocin-induced diabetes at 6 months duration (proteinuric phase) and at 7 days (pre-proteinuric phase). In addition, the effects of anti-proteinuric drug therapies were also assessed in long-term diabetic rats, treated with either the angiotensin-converting enzyme inhibitor perindopril, or the blocker of advanced glycation end-product formation, aminoguanidine. Nephrin expression was determined using quantitative real-time PCR and in situ hybridization.. When compared with control animals, nephrin expression was reduced in the late proteinuric phase (45% reduction vs controls, P<0.01) but not in the early, pre-proteinuric phase of experimental diabetic nephropathy. While ACE inhibition and aminoguanidine both reduced proteinuria, only the former attenuated the diabetes-associated reduction in nephrin expression.. These findings suggests that reduction in nephrin may be a determinant of glomerular hyperpermeability in diabetic nephropathy. Attenuation of these changes with ACE inhibition suggest that this mechanism may contribute to the anti-proteinuric effects of this, but not all classes of drug which reduce urinary protein in diabetic nephropathy.

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Base Sequence; Diabetes Mellitus, Experimental; Diabetic Nephropathies; DNA Primers; Guanidines; In Situ Hybridization; Male; Membrane Proteins; Mutation; Perindopril; Proteins; Proteinuria; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger